Evolution of human diversity. The history of Homo sapiens

Transcription

1 Evolution of human diversity The history of Homo sapiens!1

2 The primates Gibbon Orangutan Gorilla Bonobo Chimpanzee Human Human Chimpanzee Gorilla Orangutan Gibbon Macaque Millions years ago!2 Macaque Orangutan Gorilla Bonobo Chimpanzee Human

3 The last most recent common ancestor of humans and chimps 6 7 MYA fossils Problems assigning fossils to lineages 5 6 MYA sequence comparisons Different models give different results (up to 2x) Not earlier than 8 MYA As distant from humans, as from chimps we do not come from chimps or any other modern primate!3

4 Complex relations Many primate fossils found, some existed at the same time Difficult to establish phylogeny Ancestors or side lineages?!4

5 Sahelanthropus tchadensis - Toumaï Close to the MRCA of humans and chimps? Skull the size of chimp, but proportions more human About the time of speciation Could be a side lineage? Only a fragment of one skull found ~ 6-7 MYA!5

6 Orrorin tugenensis Discovered: 2001 ~ 5-6 MYA Ancestor of Homo? If so, was Australopithecus a side lineage? Bipedal? Some characteristics more human-like than Australopithecus based on bone structure at least partially Habitat forest or savanna? forest or border!6

7 Ardipithecus ramidus - Ardi Discovered in 1994, published in MYA Oldest hominin At least partially bipedal Ancestor of Australopithecus (?)!7

8 Ardipithecus ramidus - Ardi!8

9 Ardipithecus!9

10 Debate It is difficult to assign the older fossils to a lineage human lineage (hominins)? chimpanzee lineage? another lineage, with no surviving descendants!10

11 Evolution is not a straight line!!11

12 Australopithecus Many species found gracile and robust 4 2 MYA Most famous: A. afarensis Lucy (~3.6 mln lat) Mrs. Ples A. africanus The Taung child A. boisei - Olduvai!12

13 Australopithecus sediba Described in 2010, Age: ~ 2 MY Many traits between Australopithecus and Homo!13

14 Australopithecus sediba Skull volume closer to Australopithecus (~420 cm3), but some morphological traits closer to Homo - lateral asymmetry language?!14

15 Human ancestry? Australopithecus afarensis -> Homo habilis A. sediba side lineage! A. africanus -> A. sediba -> Homo A. afarensis side lineage!15

16 Homo ~ 2.3 MYA older than A. sediba one had to be a side branch The Olduvai culture tools (1.9 MYA) Homo habilis Homo erectus, H. ergaster ( pithecanthropus ) 1.5 MYA, extinct YBP First to leave Africa First to use fire Hunting (spears) Social structures Narzędzie sprzed 1,8 mln. lat z Olduvai British Museum!16

17 !17

18 Homo Fossils found in Republic of Georgia (Dmanisi) (~1.8 MYA) suggest that H. habilis, H. ergaster and H. rudolfensis could be the same species as H. erectus Based on morphological variation (no ancient DNA that old)!18

19 The cradle of humanity Australopithecus afarensis (Lucy) oldest Homo fossils (a jawbone ~ 2.3 MY) Australopithecus, Homo habilis, H. erectus, H. sapiens Australopithecus africanus A. sediba!19

20 The cradle of humanity!20

21 !21

22 The first migrations from Africa!22

23 About 2 MYA!23

24 Multiregional hypothesis = regional continuity!24

25 Multiregional evolution Human ancestors left Africa ~ 2 million years ago and evolved in parallel on different continents Gene flow (continuity) between regional populations if that were the case, TMRCA of modern humans should be ~ 2 MYA mtdna studies showed TMRCA ~ years!25

26 The OAR model (Out of Africa Replacement)!26

27 OAR Out of Africa ~ an ancestral population (already anatomically modern H. sapiens) migrated from Africa to other continents New migrants displaced the previous hominids, without mixing and drove them to extinction All modern humans are descendants of this last wave of migration!27

28 mtdna polymorphism mtdna is highly polymorphic inherited as a single genetic unit (uniparental inheritance) sets of polymorphism inherited together as haplotypes haplogroups (clusters of haplotypes sharing common polymorphisms) correlate with population history - used in anthropology, forensics etc.!28

29 mtdna haplogroups!29

30 mtdna tree!30

31 !31

32 Y chromosome haplogroups!32 Jobling & Tyler-Smith (2003) Nature Rev. Genet. 4,

33 !33

34 !34

35 Conclusions mtdna and chromosome Y trees are both rooted in African populations TMRCA years Supports OAR (recent African descent)!35

36 Human genetic diversity is low Two chimpanzees (e.g. Central and Western African) have up to 5 x more genetic differences than most distant humans Human genetic diversity highest in Africa Bottlenecks Migrations - serial founder effect Natural disaster years ago (Toba volcano)? Population reduced in Africa before migrations (~ years ago, climate change)?!36

37 Population bottleneck An episode of reduction in population size, leading to reduced allelic diversity!37

38 Founder effect A new population started by a small subgroup of original population can have radically different allele frequencies Some rare human genetic diseases are frequent in particular isolated populations Reduction in human genetic diversity serial founder effect genetic diversity decreases with increasing distance from African ancestors!38

39 The island of the colorblind In 1775 the Pingelap atoll was devastated by a typhoon, killing ~90% of the population, ~20 people survived One of them was the ruler Nahnmwarki Mwanenised, who was a carrier of the rare autosomal recessive achromatopsia Currently 10% of islanders are colorblind, a 30% are carriers In the USA the incidence of achromatopsia is 1: Achromatopsia (nonfunctional cones) is not daltonism!!39

40 Recent changes in diversity The Star cluster of Y haplotypes in Mongolia ~1,000 ( ) years ago Currently in ~8% men in Central-Eastern Asia, ~0.5% worldwide Genghis Khan?!40 Zerjal et al. (2003) Am. J. Hum. Genet. 72,

41 Neanderthals Earliest fossil traces (Asia) ~ years b.p. Lived in Europe, extinct~ years b.p. Modern humans colonized Europe~ years b.p. Were Neanderthals ancestors of Europeans, did they interbreed with humans?!41

42 Neanderthals Human and Neanderthal lineages split ~ years ago Was in Europe before H. sapiens (earlier migration) Culture (burials), tools, probably speech Wikimedia commons, Anthropological Institute, University of Zürich!42

43 !43

44 The Neanderthal genome project mtdna fragments of several specimens (1997) ~ 10 6 bp of ndna (2006) 60% of nuclear genome (2010) more complete genome of several specimens (2013)!44

45 mtdna!45 Krings M., Stone A., Schmitz R.W., Krainitzki H., Stoneking M., and Pääbo S. (1997), Cell, 90:19-30.

46 mtdna tree!46 Knight A. (2003): Journal of Human Evolution, 44:

47 mtdna - conclusions Neanderthal mtdna outside the human tree Not closer to Europeans than to other populations No sign of interbreeding in Neanderthal maternal lineage Low population genetic diversity!47

48 ndna results - evolution!48

49 Genome sequencing conclusions Human and Neanderthal lineages split long before the last common ancestor of modern humans Neanderthals were not our ancestors What about interbreeding?!49

50 The 2010 genome analysis Confirmed the final split of lineages ~ years ago SNP polymorphic sites Neanderthal alleles found in human genomes, but only from Europe, Asia, and Oceania No Neanderthal SNPs in African genomes!50

51 Did humans and Neanderthals interbreed? ~ 4% of polymorphisms in Eurasian genomes of Neanderthal origin! Low level of interbreeding between Neanderthals and ancestors of Eurasian populations!51

52 Scenarios Amount of Neanderthal alleles is the same in Europe, Asia and Papua New Guinea Interbreeding with the ancestors of E, A i PNG, somewhere in the Middle East Intermixing was rare wavefront effect rapid expansion of migrant population amplifies the alleles intermixed from the encountered local populations!52

53 Not just Neanderthals Fossils from the Denisova cave (Altai mountains) Contemporary of Neanderthals probably a sister group Traces of interbreeding in human populations from Oceania intermixing episode during migration to SE Asia!53

54 Interbreeding Recent Denisovan genome sequence (2013) suggests interbreeding with H. sapiens, H. neanderthalensis and a fourth unknown hominid!54

55 The Sima de los Huesos mystery DNA from a years old bone fragment from Northern Spain- mtdna closer to Denisovan than Neanderthal bones and teeth look closer to Neanderthal ancestor of Denisovans and Neanderthals? a separate lineage?!55

56 !56

57 Conclusions OAR is essentially supported, but more complex than thought Migrants could interbreed with earlier populations!57

58 Not so simple story mtdna of modern Europeans is different from European mtdna from before years ago neolithic migrations (~7 000 YBP) subsequent migrations also early and late Neanderthal mtdna is different significant inbreeding among Neanderthals - small population size (cause of extinction?)!58

59 European prehistory First settlement from Africa (~ YBP) Glacial period - repeopling from southern refugia and postglacial recolonization ( YBP) Neolithic farmer migration from Near East (7 000 YBP) later migrations Indo-European migration YBP!59

60 European prehistory 3 ancestral populations West European Hunter-Gatherers (earliest) Ancient North Eurasians (Siberia), also contributed to Native Americans Early European Farmers (Middle East, Neolithic revolution) Based on ancient DNA sequences from year old skeletons!60

61 !61

62 Descendants of the first Europeans? All European populations are a mixture of pre-neolithic (hunter-gatherer) and neolithic (farming) ancestry The only signs of continuity from pre-neolithic times - the Basque!62

63 Out of Africa - human genetic diversity!63

64 Genetic diversity gradient!64

65 More than genes Genetic diversity correlates with language diversity!65

66 The diversity of languages classification based on phonemes (sounds) phoneme diversity!66 Atkinson, Science (2011) 332:

67 The spread of language!67

68 The question of race Lewontin s argument variation within group higher than between groups traits allowing to distinguish races - ~6% of all variability Traditional classification of races is based on traits that are not a good measure of genetic similarity skin colour (~6 genes), nose and eye shape under selection Some traits do show correlation (covariance) gradients, not groups A continuum of genetic variability reflecting population history is real!68

69 The question of race A continuum of genetic variability reflecting population history is real But it does not allow to create meaningful divisions A monophyletic group that would include all the descendants of a common ancestor of Africans would also include all non-africans!69